This disclosure is directed to a method to form crossing under rivers and other natural barriers. The procedure accomplishes a river crossing which is the term that will be applied to crossing under a river with a pipeline. This term is sufficiently broad to also include rivers, highways, landing strips at airports and any other number of surface barriers. It may also be necessary to pass under large buildings where it is not possible to do tunneling or digging under the buildings. It is not uncommon to require river crossings of only a few hundred feet. For instance, crossing under rivers and swamps may require that a pipeline be buried perhaps 40 to 60 feet deep, perhaps 2,000 or 3,000 feet in length, and thereafter be restored to the normal grade position.
It is common to locate a pipeline about 4 to 8 feet below the surface. With undulating surfaces, the pipeline is still laid in a ditch or trench which is formed with that depth. The ditch will rise and fall as the terrain varies. There are times, however, when that is not so easily done. Trenching machines that are used to form pipelines must operate with a certain amount of right of way. Moreover, they operate on the surface, digging an open trench. It is not possible to run a trenching machine across a paved multiple lane highway. It is not possible to run a trenching machine over several railroad tracks, and it is exceedingly difficult to operate a trenching machine in a swamp. Even if the swamp water is only 2 or 3 feet deep, it normally is accompanied by a mud layer which makes heavy equipment manipulation difficult in the area.
Many situations can be encountered in long distance pipelines where river crossings must be done. A river crossing heretofore has involved the insertion of a string of drill pipe, not joints of a pipeline, into a well borehole by a drilling rig laid on its side, so to speak, and the string of drill pipe rotates a drill bit to form a hole which is more or less horizontal, not vertical. Ordinary drilling of wells involves vertical drilling from the surface. This departs immediately from that requirement, and involves drilling at a highly inclined angle, even approaching the horizontal at the surface where the drill string enters the earth. In drilling a typical well, the first several hundred feet are normally drilled vertically. A good deal of speed can be accomplished at the start. That, however, is not the case with a river crossing. Rather, the drill bit and drill string are inclined by inclining the derrick so that the initial launch of the drill pipe into the earth is nearly horizontal. To be sure, the hole formed by this approach angles downwardly to dive under the river crossing. It will, however, deflect later so that it turns back towards the surface on the far side of the river or other barrier. There is an entrance point on the near or first bank and an exit point on the far or second bank. Once the entrance and exit points have been established, the pipeline is installed with welded pipe in the well borehole which defines the river crossing. Because this involves two different kinds of pipe which have two different types of construction, it is necessary to position in the well borehole a string of pipe which is sized and constructed consistent with pipeline construction techniques. More will be noted concerning that below. The term xe2x80x9cdrill pipexe2x80x9d will be used to refer to pipe which is normally used in drilling a well borehole. Drill pipe terminates with a pin and box connection for easy threaded engagement. These pin and box connections typically include API standard threaded connections, or any of the several premium connections now available. There are premium threads which provide an enhanced mode of connection. Suffice it to say, pipe used in a pipeline is not joined by threaded connections. Rather, pipe line joints are formed by welding. The welded pipe is joined by welding in the field typically with welding machines which form a bead fully around the pipe so that there is no chance of leakage. In addition, the welded pipe is coated with some kind of corrosion protection material. For many years, the corrosion protection comprised a layer of tar and felt paper. There are other more modern coatings which are placed on the steel pipe. The pipe joints making up the pipeline must be protected from chemical reaction with the earth. Without this protection, the pipe will corrode more rapidly and the value and benefit of the pipe will be lost much sooner due to this corrosion.
The present disclosure sets forth an alternate use of the apparatus which is set forth in U.S. Pat. No. 5,821,414. It is been discovered that this apparatus can be installed in the form of a sonde which is placed in the drill pipe above the drill bit. This sonde includes a sealed chamber which encloses the measuring instruments. Preferably, it uses a pair of accelerometers which are mounted in a common horizontal plane transverse to the central axis of the sonde. They are positioned at right angles so that one will be described as the X-axis accelerometer or simply the X-accelerometer, and the other becomes the Y-accelerometer. It is theoretically possible to install a third accelerometer which is the Z-accelerometer, and to position along the axis of the sonde. That represent a data which would be otherwise redundant. While it can be included for added data to provide reduction of error, it can be omitted as the case may be. In another aspect, the equipment uses a gyroscope which is known as dual axis rate gyroscope. As before, the spin axis is aligned with the axis of the sonde. The dual axis rate gyro will be discussed in some detail below.
The apparatus of the present disclosure is summarized as a sonde which is adapted to be lowered or otherwise installed adjacent to the drill bit on a string of drill pipe used in a river crossing. It is located at that position so that it can provide information regarding the pathway achieved during drilling. It is used to monitor the pathway by providing that data in the form of azimuth and inclination. This enables steering of a smooth pathway. It provides data at the well head which enables control of the drilling process. Through the use of a bent sub and a jet flow of drilling mud through the bit, the pathway can be changed. Alternately, it can be used above a mud motor which cooperates with a steering tool to redirect the pathway.